An important indicator of God's will in our lives is the "inward witness of the Holy Spirit." Scripture talks to us about the Holy Spirit who indwells any one who receives and trusts in Christ. Central to a believer's life is following the leading and guiding of the Spirit of God (John 16:13; Romans 8:14; Galatians 5:18).
It's impossible to physically prove the guidance of the "inward witness of the Holy Spirit." I say this because it's an experience that takes place within the heart of a believer. It's personal. It represents internal impressions that are not normally audible or perceivable such as wind or fire. So, such will be beyond our comprehension or ability to describe fully into words.
"I have peace inside" is a most common expression I hear from others when they talk about God's leading in their lives. It's true. The Bible supports this. Colossians 3:15 says, "Let the peace of Christ rule in your hearts." Paul is saying in this verse that when you allow the peace of God to rule in your decisions, God reveals His individual will to you.
Yet this is precisely what our materially driven society finds unacceptable. For it fears fanaticism and subjectivism. But the Holy Spirit's inward witness and personal subjectivism need not be the same. In fact, they are quite different.
The challenge then that faces us is to be fully obedient to the supernatural direction of the Holy Spirit. We experience the "peace of God" when we allow the Holy Spirit to speak to our hearts and follow his guiding impulse. On the other hand, we experience restlessness and worry when we move outside of His direction.